The present invention relates to industrial control systems and, in particular, to a method and apparatus for communicating transactions between an industrial controller and a programming interface.
This section of this document is intended to introduce various aspects of art that may be related to various aspects of the present invention described and/or claimed below. This section provides background information to facilitate a better understanding of the various aspects of the present invention. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Industrial controllers are special purpose computers used for controlling industrial processes or manufacturing equipment. Under the direction of a stored program, the industrial controller examines a series of inputs reflecting the status of the controlled process and changes outputs affecting the control of the process. The inputs and outputs are most simply binary, that is “on” or “off”, however analog inputs and outputs taking on a continuous range of values are also used. The binary inputs and outputs may be represented by single bits of data, the analog inputs and outputs may be represented by multiple bit data words.
The various components of an industrial controller are often spatially distributed about a factory or manufacturing facility to be interconnected by one or more communication networks. These communication networks are characterized by being highly reliable and by delivering data with a minimal and well defined delay, as is required for real-time control. A number of different communication networks are commonly used in the industrial controller art including but not limited to: ControlNet; DeviceNet and EtherNet whose specifications are published and whose protocols are used broadly by a number of manufacturers and suppliers. These communication networks differ from one another in physical aspects, for example, the type of media (e.g., co-axial cable, twisted pair, light fiber, etc.); the protocols of its operation, (e.g., Baud rate, number of channels, word transmission size, use of connected messaging, etc.) and how the data is formatted and how it is collected into standard messages.
A common component of the industrial controller is an input or output (I/O) module which accepts data for a central control computer from the controlled process or machine, and provides data from the central control computer to the controlled process or machine. I/O modules are typically remote from the central control computer and connected via a communications network as described above.
In some applications, I/O modules may be added while the industrial controller is actively controlling a process. The nature of the process may be such that interrupting the process to reprogram the controller would cause costly downtime or product defects. To configure the industrial controller to recognize the added I/O module, the control programs stored in the controller are modified to create various data objects and communication links.
In some industrial control systems, a workstation computer executes a software application to provide a programming interface for accessing and modifying the control program of the industrial controller to implement programming changes such as adding an I/O module, for example. To implement the desired change, a series of discrete commands are communicated from the workstation software to the controller to establish the required entities. In some cases, a power cycling event or the loss of the communication link between the workstation and the controller may disrupt the series of commands midstream. The series may also be disrupted if the controller cannot process one of the commands, for example due to the state of an object being modified or a lack of memory space for an object being added.
In cases where the series of commands is interrupted or fails, it is difficult to clean up the partially completed process for instantiating the added module or program change. It may not be feasible to shut down the process to allow the last known good image to be reloaded onto the controller. Hence, the clean up may need to be performed manually, which is time-consuming, potentially expensive, and imprecise. For example, all of the objects created in the controller may not be properly removed during the clean up process. These artifacts may lead to wasted storage space or even system instability.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.